**Interval notation** is a method for writing intervals on a number line. Solutions can be written using brackets and parentheses.

For **<** and > use ( )

For use [ ]

Always use a ( ) with **Infinity**

For example, how would you write the following inequality?

**x > 3**

Always write from left to right.

There is a greater than sign so use a parenthesis and it goes to infinity so use a parenthesis sign.

( 3, ∞ )

Let’s look at another example.

x ≤ 2

Remember, you read from left to right.

There is a less than and equal to sign so it goes to infinity on the left, and then a 2 and it is less than and equal to so it will have brackets.

**( ∞, 2 ]**

In summary,** interval notation** is a method for writing inequalities using paranthesis and brackets. **Parenthesis** are used with less than and greater than plus infiniti and **brackets** are used with greater than and equal to plus less than and equal to.